If you're a Mac fan, a new i7 iMac 27" with one of the new Focusrite interfaces may be a great move. Especially if you get the iMac with the extra internal hard drive for recording(which usually means an SSD for system). If you want to go PC, then a custom built i7 machine is the way to go, or look at some of the computer builders that specialize in DAW setups like Sweetwater or Rain(or is it Rainsong?). Anyway, going PC requires more homework up front, but can save a lot of cash. Its possible that any old sessions you may have, won't be retrievable
(just in case that matters). If the old system is still complete and will run, you could open sessions, consolidate all audio back to 00:00:000 and export. Then the audio could likely be imported into a new system(AFAIK, the new Macs can still read SD II files).